The present disclosure generally relates to thin film varactor device structures and, in particular, to nanostructured dielectric thin-film varactors having a parallel capacitor architecture.
High K tunable, microwave dielectrics such as barium strontium titanate (BaxSr(1-x)TiO3), or BST, are gaining acceptance in microwave integrated circuits due to a large need for tunable/reconfigurable circuits. Semiconductor varactor diodes and PIN diodes can have relatively large Q below 10 GHz, but the Q can drop down drastically above 10 GHz making them less attractive for applications above 10 GHz. Radio-frequency (RF) microelectromechanical system (MEMS) switches can offer high Q at microwave and millimeterwave frequencies, but can be complex in nature, and the slow speed of switching can be undesirable for many applications. Ferroelectric varactors can be characterized by fast switching speed, ease of integration with silicon (Si) monolithic microwave integrated circuits (MMICs), and can have reasonable Q at microwave and millimeter-wave frequencies.
Ongoing needs remain for an improving RF performance over a broad frequency range that allows for larger signal isolation at lower frequencies.